Systems involving heat or mass transfer are crucial to our industrialized society. Examples of such systems include: power generation, chemical processing systems, and heating and cooling systems. For more than 100 years, scientists and engineers have endeavored to increase the efficiency or reduce the cost of these systems.
Battelle, Pacific Northwest National Laboratories, and others have been using microtechnology to develop Microsystems for carrying out processes that had previously been conducted using far larger equipment. These systems, which contain features of about 1 millimeter (mm) or less, may potentially change heat and mass transfer processing in ways analogous to the changes that miniaturization have brought to computing. Microsystems can be advantageously used in small scale operations, such as in vehicles. Microsystems that can be economically mass-produced can be connected together to accomplish large scale operations.
The production of hydrogen from hydrocarbon fuels, for use in fuel cells, is one example of an application that has been proposed for microsystems. Fuel cells are electrochemical devices that convert fuel energy directly to electrical energy. For example, in a process known as steam reforming, a microsystem can convert a hydrocarbon fuel (or an alcohol such as methanol or ethanol) to hydrogen and carbon monoxide. The hydrogen is fed to a fuel cell that reacts the hydrogen with oxygen (from the air) to produce water and an electric current. The CO could, in a reaction known as the water gas shift reaction, be reacted with water to produce additional hydrogen and carbon dioxide.
A second application has been proposed for delivering hydrogen to fuel cells that involves liquid organic hydrogen carriers (LOHCs). A chemical reactor is operated that removes molecular hydrogen from a LOHC through one or more dehydrogenation reactions, and the hydrogen is consumed in a fuel cell to produce electricity. The spent dehydrogenated LOHC is recovered and returned to a central facility where reverse hydrogenation reactions reload hydrogen onto the LOHC. By this process, the LOHC serves as a carrier for delivering hydrogen to fuel cells or other power systems in distributed applications, such as on fuel cell powered vehicles.
Despite long and intensive efforts, there remains a need for energy efficient and cost effective systems for carrying out operations involving heat or mass transfer. There is also a need for compact systems or reactor systems for generating large volumes of gas from a liquid stream, for producing large volumes of liquid from a gaseous stream, and for performing a reaction between a gaseous stream and a liquid stream.